1. Field of the Invention
The present invention relates to a brake band which is employed in a wet type band brake apparatus for an automatic transmission of an automobile or the like.
2. Description of the Related Art
A band brake apparatus for an automatic transmission gives a higher static torque capacity than a multi-plate brake apparatus having the same dimension does. Since the band brake apparatus gives different torque capacities in directions for braking a drum, it gives a favorable transmission characteristic as a releasing element in an up-shift operation. Hence, the band brake apparatus has been used widely as a reaction force element. In such a band brake apparatus, a drum is braked by pressing a brake band to the drum. The band brake is one which is illustrated in FIG. 17.
For instance, the conventional brake band comprises a band 100 which is made of metal and which is wound in a ring shape, and a tape-shaped lining 200 which is connected to an inner peripheral surface of the band 100, as illustrated in FIG. 17. The band 100 is provided with a plurality of oil holes 101 which penetrates to the outside, and it is also provided with brackets 102 and 103, to which a tightening force acts, at its both ends. Further, in this conventional brake band, two linings 200 are disposed parallelly at a predetermined interval. Furthermore, a groove 201 is formed between the two linings 200 so as to expose the oil holes 101.
In a band brake apparatus which employs the conventional brake band, oil is supplied between the drum and the linings 200 by way of an outer peripheral surface of the drum. Thus, lubrication is carried out during braking operation, and heat generated by friction is cooled down. The oil which has deprived the heat and which is heated accordingly is expelled to the outside through the oil holes 101.
Recently, an automatic transmission has been down-sized and an engine has been improved to a higher output one. Accordingly, a brake band has come to be used in a harsher environment. Namely, a sliding speed between the drum and the lining has increased to a higher speed, and consequently a frictional force which acts on the lining has increased. As a result, it is necessary to improve the heat resistance of the lining. Here, it is effective to improve the cooling efficiency of the oil in order to improve the heat resistance of the lining.
In Japanese Unexamined Utility Model Publication (KOKAI) No. 135,031/1988, for instance, a brake band is proposed. The brake band includes a lining including grooves which extend in an axial direction of a drum as well.
In addition, the applicant of the present invention disclosed a brake band in Japanese Unexamined Utility Model Publication (KOKAI) No. 87,137/1990. The brake band includes inclined grooves in an inner peripheral surface of a lining, and it includes oil holes which are disposed at both ends of the grooves and which penetrate to the outside. By communicating the grooves with the oil holes in this manner, the oil heated by a frictional heat can be expelled to the outside smoothly. Hence, the heat resistance of the lining is improved remarkably.
The applicant of the present invention has kept on developing the brake band which is disclosed in Japanese Unexamined Utility Model Publication (KOKAI) No. 87,137/1990 further, and the applicant has found that there sometimes occurs the judder during engine braking.